: It is widely appreciated that glutamate-triggered acute neuronal injury is dependent on calcium entry into neurons and that the most rapid form of injury is mediated by the activation of N-methyl-D-aspartate receptors. However, in previous studies that have used in vitro models of neuronal injury it has been difficult to account for the specificity of the neurotoxic effects of NMDA receptor activation because of the difficulty in distinguishing toxic and non-toxic intracellular calcium changes. In re-evaluating the studies that link calcium changes to neuronal injury it becomes apparent that it is necessary to reconsider the issues of the magnitude of calcium changes that are associated with injury because previous studies may not have provided accurate results. In addition, unappreciated issues of the selectivity of the commonly used fluorescent dyes for intracellular divalent cations suggest that magnesium and zinc should also be considered as candidate neurotoxins in excitotoxic injury. The long-term goal of these studies is to understand the ionic mechanisms by which glutamate kills neurons. The applicants plan to: determine if non-NMDA receptor agonists induce acute neuronal injury if the magnitude of the calcium change they induce is increased; determine if the magnitude of the intracellular Mg change in neurons is stimulated by glutamate, and how would this alter mitochondrial function; determine the magnitude of intracellular zinc changes and how they may relate to neuronal injury; and, to determine the mechanisms neurons are protected from zinc-mediated injury. There are a number of potentially important interrelationships between the various cation-mediated forms of injury, and the proposed approach is to investigate these relationships, and, also to exploit the similarities in methodology that can be adapted to measure each ion of interest.